In a typical radio communications network (for example, a Long Term Evolution (Long Term Evolution, “LTE” for short) network), an uplink shared data channel (Shared Data Channel) is selected based on a scheduling/grant (Scheduling/Grant) mechanism and a base station (Base Station, “BS” for short) takes full control. In the mechanism, user equipment (User Equipment, “UE” for short) first sends an uplink scheduling request to the BS. When receiving the request, the BS sends an uplink grant to the UE to notify the UE of an uplink transmission resource that is allocated to the UE. Accordingly, the UE transmits data on the granted uplink transmission resource.
Massive user access is one of typical application scenarios of a next-generation communications network. During access of a large quantity of users, if the foregoing scheduling/grant mechanism is still used, on one hand, excessive signaling transmission overheads are caused and a BS is under great pressure to allocate and schedule resources, and on the other hand, a notable transmission latency is caused. In view of this, a grant free (Grant Free) transmission scheme is used in the next-generation communications network to support access of a large quantity of users. In the grant free transmission scheme, the BS defines, in an uplink transmission resource, an access region for a contention transmission unit (Contention Transmission Unit, “CTU” for short). The UE accesses the uplink transmission resource in the region in a contention-based manner without the need of following the scheduling/grant mechanism.
To successfully perform uplink grant free transmission, the UE should first determine a CTU resource for uplink transmission. The CTU resource may be determined based on a pre-determined UE-CTU mapping rule known to both the UE and the BS. The UE may implicitly learn of the mapping rule that is, for example, stipulated by a standard or implemented by a firmware. Alternatively, the BS may explicitly notify the UE of the mapping rule by using higher-layer signaling. For example, different mapping rules may be first defined in a standard, and the BS then informs, by using signaling, the UE of a sequence number of a corresponding mapping rule.
Different UEs are allowed to perform uplink access transmission by using a same characteristic wave (the characteristic wave may be referred to as a signature). The signature may be considered as a code resource. A conflict occurs when multiple UEs use a same signature to synchronously access a same time-frequency resource (that is, a same time-frequency-code resource). A corresponding advanced detection method is required to resolve the conflict. When the multiple UEs that use the same time-frequency-code resource further use a same pilot, it is usually considered that a conflict cannot be resolved by using only the detection method. In this case, a special conflict avoidance or resolution mechanism such as remapping or retransmission needs to be used together. To avoid a conflict between particular UEs or over a particular CTU, some UEs may be remapped to a new CTU resource.
For the foregoing grant free transmission for access of a large quantity of users, because multiple UEs are allowed to perform contention-based transmission on a same CTU resource, a contention conflict is caused, and reliability of the grant free transmission is reduced. To ensure low-latency and high-reliability grant free transmission, it is necessary to provide extra transmission protection to some UEs having a special service requirement.